1. Field of the Invention
The present invention relates to a ball nose end mill on which at least one throwaway insert is mounted.
2. Background Art
An example of such a ball nose end mill with a throwaway insert is disclosed in Published Japanese Translation No. H11-500670 of the PCT International Application.
The throwaway insert includes a cutting edge which is formed substantially as an arc of a quarter circle along a ridge between an upper face and a side face, and which includes a plurality of sinusoidal portions so as to reduce cutting force, and so as to improve ability to break and remove chips produced from a workpiece.
In the sinusoidal cutting edge, all concave portions and all convex portions exhibit the same depth and the same height, respectively, i.e., the cutting edge exhibits a wavy shape having a constant “amplitude” over the entire length.
When cutting of a workpiece is performed using the throwaway insert having the wavy cutting edge in a so-called “downward cutting manner” in which the axis of rotation is directed horizontally, and cutting is performed downwardly so that a cut chip has a greater thickness at the beginning of cutting than at the end of cutting, the cutting operation can be easily performed with relatively low cutting force, and chips are easily separated so that sufficient chip dischargeablity is maintained.
However, when cutting of a workpiece is performed in a so-called “upward cutting manner” in which the axis of rotation is directed horizontally, and cutting is performed upwardly so that a cut chip has a smaller thickness at the beginning of cutting than at the end of cutting, because, in this case, the thick portions of the chips at the end of cutting tend to be compressed so that the chips may not be preferably separated and may be produced continuously; therefore, sufficient chip dischargeablity may not be obtained.
In order to ensure separation of chips even when cutting is performed in an “upward cutting manner”, the depths of the concave portions, which form the wavy cutting edge, may be made greater. In this case, separation of chips can be ensured; however, the wavy cutting edge exhibits a large “amplitude” because the cutting edge is formed so as to exhibit a wavy shape having a constant “amplitude” for all concave portions and convex portions, and as a result, the strength of the cutting edge may be unexpectedly decreased. Therefore, increasing the depths of the concave portions may not be an effective solution.